Dissident republicans in south Armagh and north Louth are delivering ready-made bombs to Belfast for attacks on big targets — including Palace Barracks and the Policing Board headquarters.

A senior security source described those border regions as “the crucible” of dissident engineering activity in a nod to their bomb-making skills.

The threat level is now at its highest since the Real IRA bombing campaign of 1998, which ended in the Omagh massacre.

The source said: “It feels to us, just looking at it in every way, that this has picked up in terms of intensity and severity”, adding the threat “remains very properly at severe”.

The source said intelligence assessments show “increased communication leading to increased co-operation” among the different dissident groups, principally the two factions of the Real IRA.

“They probably still see themselves as two distinct organisations, both numerically strong, and they have people there who undoubtedly now have developed technical capabilities around improvised explosive devices, of nearly all types,” the source said.

“The main conversation is (between) the two factions — the two elements — of RIRA, something you wouldn’t have seen maybe a year-and-a-half ago,” he said.

The big security concern, after a series of failed attacks, is the obvious recent advance in the dissident bomb-making capability.

“They’re now being successful,” the source said. “We have to assume that they’ve actually worked at this in terms of successful detonation.”

He revealed that the bomb used in the recent attack on Palace Barracks contained between 50kg-60kg of homemade explosives packed inside a beer barrel. It was delivered from the border to Belfast as a “complete device”, ready for use.

One man was injured when the bomb exploded after the device was delivered to Palace Barracks in a hijacked taxi early on April 12. The bomb at the Policing Board was much bigger. It only partially detonated.

“There are a number of people with the skills,” the source said.

“We really have to work on the assumption that there is more than one person able to do this.

“You can be trained up to do this or else you can draw on the older skills. We have to work through both those investigative possibilities .”

The technology matches pre-ceasefire IRA bombs.

“Undoubtedly there are former IRA people who are deeply embedded in these (dissident) organisations,” the source said.

This, he said, is the case since the 1997 split over the Adams and McGuinness peace strategy.

“In its root it always had people who once were PIRA and they still remain embedded in it.”

The source spoke of “the shadow of Omagh” — that in their targeting and “deploying” devices dissidents are working to avoid a repeat of that 1998 slaughter.

Now, the bulk of their targeting is focused on “trying to create a tense and difficult operating environment for police officers”.

The source added that the dissidents will be very keen to disrupt “neighbourhood policing”.

“The next tier of targeting is against off-duty officers. They are targeting those readily available, which turns out to be officers still involved in the like of the GAA. It’s the people who are known within the community,” he said.

“We are going through a process right across the organisation of just making sure that all our officers, and particularly officers who have joined in the last few years, are very conscious of their own personal security..”